string: Implement strerror in terms of strerror_l

If the thread is terminated then __libc_thread_freeres will free the
storage via __glibc_tls_internal_free.

It is only within the calling thread that this matters.  It makes
strerror MT-safe.

Checked on x86-64-linux-gnu, i686-linux-gnu, powerpc64le-linux-gnu,
and s390x-linux-gnu.

Tested-by: Carlos O'Donell <carlos@redhat.com>
Reviewed-by: Carlos O'Donell <carlos@redhat.com>

NEWS

@@ -79,6 +79,11 @@ Deprecated and removed features, and other changes affecting compatibility:
   compatibility symbols to support old binaries.  All programs should use
   strerror or strerror_r instead.
 
+* Both strerror and strerror_l now share the same internal buffer in the
+  calling thread, meaning that the returned string pointer may be invalided
+  or contents might be overwritten on subsequent calls in the same thread or
+  if the thread is terminated.  It makes strerror MT-safe.
+
 Changes to build and runtime requirements:
 
 * powerpc64le requires GCC 7.4 or newer.  This is required for supporting

include/string.h

@@ -4,6 +4,7 @@
 /* Some of these are defined as macros in the real string.h, so we must
    prototype them before including it.  */
 #include <sys/types.h>
+#include <locale.h>
 
 extern void *__memccpy (void *__dest, const void *__src,
 			int __c, size_t __n);
@@ -50,6 +51,8 @@ extern int __ffs (int __i) __attribute__ ((const));
 
 extern char *__strerror_r (int __errnum, char *__buf, size_t __buflen);
 
+extern char *__strerror_l (int __errnum, locale_t __loc);
+
 /* Called as part of the thread shutdown sequence.  */
 void __strerror_thread_freeres (void) attribute_hidden;
 
@@ -113,6 +116,7 @@ libc_hidden_proto (memmem)
 extern __typeof (memmem) __memmem;
 libc_hidden_proto (__memmem)
 libc_hidden_proto (__ffs)
+libc_hidden_proto (__strerror_l)
 
 #if IS_IN (libc)
 /* Avoid hidden reference to IFUNC symbol __explicit_bzero_chk.  */

string/strerror.c

@@ -15,29 +15,11 @@
    License along with the GNU C Library; if not, see
    <https://www.gnu.org/licenses/>.  */
 
-#include <libintl.h>
-#include <stdio.h>
 #include <string.h>
-#include <errno.h>
-
-/* Return a string describing the errno code in ERRNUM.
-   The storage is good only until the next call to strerror.
-   Writing to the storage causes undefined behavior.  */
-libc_freeres_ptr (static char *buf);
+#include <locale/localeinfo.h>
 
 char *
 strerror (int errnum)
 {
-  char *ret = __strerror_r (errnum, NULL, 0);
-  int saved_errno;
-
-  if (__glibc_likely (ret != NULL))
-    return ret;
-  saved_errno = errno;
-  if (buf == NULL)
-    buf = malloc (1024);
-  __set_errno (saved_errno);
-  if (buf == NULL)
-    return _("Unknown error");
-  return __strerror_r (errnum, buf, 1024);
+  return __strerror_l (errnum, __libc_tsd_get (locale_t, LOCALE));
 }

string/strerror_l.c

@@ -20,8 +20,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
-#include <sys/param.h>
-#include <libc-symbols.h>
+#include <errno.h>
 
 static __thread char *last_value;
 
@@ -38,8 +37,9 @@ translate (const char *str, locale_t loc)
 
 /* Return a string describing the errno code in ERRNUM.  */
 char *
-strerror_l (int errnum, locale_t loc)
+__strerror_l (int errnum, locale_t loc)
 {
+  int saved_errno = errno;
   char *err = (char *) __get_errlist (errnum);
   if (__glibc_unlikely (err == NULL))
     {
@@ -48,11 +48,16 @@ strerror_l (int errnum, locale_t loc)
 		      translate ("Unknown error ", loc), errnum) == -1)
 	last_value = NULL;
 
-      return last_value;
+      err = last_value;
     }
+  else
+    err = (char *) translate (err, loc);
 
-  return (char *) translate (err, loc);
+  __set_errno (saved_errno);
+  return err;
 }
+weak_alias (__strerror_l, strerror_l)
+libc_hidden_def (__strerror_l)
 
 void
 __strerror_thread_freeres (void)

sysdeps/mach/strerror_l.c

@@ -42,7 +42,7 @@ translate (const char *str, locale_t loc)
 
 /* Return a string describing the errno code in ERRNUM.  */
 char *
-strerror_l (int errnum, locale_t loc)
+__strerror_l (int errnum, locale_t loc)
 {
   int system;
   int sub;
@@ -86,6 +86,8 @@ strerror_l (int errnum, locale_t loc)
 
   return (char *) translate (es->subsystem[sub].codes[code], loc);
 }
+weak_alias (__strerror_l, strerror_l)
+libc_hidden_def (__strerror_l)
 
 /* This is called when a thread is exiting to free the last_value string.  */
 void